Digital broadcast receiving apparatus

ABSTRACT

The digital broadcast receiving apparatus according to the present invention includes a tuning unit for outputting normal image data for performing a normal reproduction operation corresponding to a user selected channel, a memory unit for outputting background image data for performing a background reproduction operation when the normal reproduction operation cannot be performed, a data selector for receiving the normal image data and the background image data and outputting one of the normal image data and the background image data, and an MPEG video decode unit for decoding image data output by the data selector to generate an image signal. The tuning unit successively receives the respective channel selected in the background independently of the user selection, and stores the background image data corresponding to the respective channels in the memory unit.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a digital broadcast receivingapparatus, and more specifically, to a digital broadcast receivingapparatus for receiving a digital television broadcast.

[0003] 2. Description of the Background Art

[0004] In recent years, the digitization project of television broadcastis rapidly progressing worldwide. Particularly, in the field of digitaltelevision broadcast, the use of MPEG2 (Moving Picture Experts Group 2),which is an international standard of data compression/decompression,enables transmission of a plurality of channels with a single repeaterso that the number of channels can be significantly increased. As aresult, convenience for the user is expected to improve significantly.

[0005] In receiving digital television broadcast, there is a need todecode compressed coded data to obtain the actual image signal and audiosignal.

[0006]FIG. 11 is a schematic block diagram representing an arrangementof a general digital television broadcast receiving system.

[0007] Referring to FIG. 11, a digital television broadcast receivingsystem 1 includes an antenna 2 for receiving RF signals which areairwaves, and a detection-demodulation unit 3 for performing detectionand demodulation of the RF signals according to a channel selectioninstruction from the user. Detection-demodulation unit 3 outputstransport stream data (hereinafter, also simply referred to as TS data)according to the MPEG2 standard. The TS data is formed as one datastream into which coded data respectively corresponding to an imagesignal, an audio signal, and a data signal are multiplexed.

[0008] Digital television broadcast receiving system 1 further includesa TS separating unit 4 for separating the multiplexed TS data, an audiodecode unit 5 for decoding audio coded data received from TS separatingunit 4, and a video decode unit 6 for decoding image coded data receivedfrom TS separating unit 4.

[0009] Audio decode unit 5 and video decode unit 6 executes decoding ofthe compressed coded data according to the MPEG2 standard. An audiosignal and an image signal respectively are output from audio decodeunit 5 and video decode unit 6 and transmitted to an audio output unit 7and an image display unit 8. As a result, from the RF signals receivedby antenna 2, the image signal and the audio signal corresponding to theuser channel selection can be output to image display unit 8 and audiooutput unit 7.

[0010] In addition, although not shown in FIG. 11, data signal that isincluded in the TS data can also be output to image display unit 8 byexecuting decoding based on the MPEG2 standard.

[0011] In the digital television broadcast, however, it is inherentlydifficult immediately to display a real time image corresponding to theairwaves upon power-on of the receiving apparatus or upon switching ofthe channel selection by the user (hereinafter, also described simply as“upon channel switching”). During this period, no image is displayed onimage display unit 8 so that there is a possibility that unnecessaryanxiety and stress may be caused to the user.

[0012] Returning to FIG. 11, in order to start data demodulation indetection-demodulation unit 3, it is required that the received data ofat least a prescribed amount that is the minimum required for executionof error correction be accumulated. Consequently, upon power-on or uponchannel switching, outputting of TS data from detection-demodulationunit 3 is delayed for the period during which the prescribed amount ofreceived data is accumulated. In addition, in decoding the image codeddata, there is a possibility of delay being generated in image displaydue to the nature of the MPEG2 standard.

[0013]FIG. 12 is a schematic diagram related to the description of acomposition of image coded data according to MPEG2.

[0014] Referring to FIG. 12, the image coded data according to MPEG2(hereinafter, also simply referred to as MPEG2 image coded data) isexpressed as bit stream data having a hierarchical arrangement.Particularly, in the MPEG2 standard, data corresponding to severalpictures are treated as a prescribed segment called GOP (Group ofPictures), and the GOP structure is adopted which allows random accessby the unit of GOP.

[0015] In other words, MPEG2 image coded data is formed by a pluralityof GOPs, and a sequence header SH is provided corresponding to each GOP.Information such as data size is recorded in the sequence header SH, andthe sequence header SH is used, for instance, to locate the start ofrandom access performed by the unit of GOP.

[0016] One GOP includes picture data generated by compression-coding aprescribed number of original pictures. In the MPEG2 standard, thepicture data can be categorized into the following three picture typesbased on the compression coding scheme of the original pictures: an Ipicture (Intra-coded picture), a P picture (Predictive-coded picture),and a B picture (Bidirectionally predictive-coded picture).

[0017] The I picture, also referred to as an intra-coded picture,involves coding of one original picture alone whose information isindependent of other original pictures. Thus, the I picture isindependent of other pictures that precede or succeed it and can bedecoded by itself. Each GOP is formed such that it includes at least oneI picture.

[0018] The P picture, also referred to as an inter-framepredictive-coded picture, utilizes an I picture or a P picture of anearlier time already decoded as a predicted image (image that serves asa reference in order to take the difference) and involves coding of themotion-compensated difference between the original P picture and thepredicted image.

[0019] The B picture, also referred to as a bidirectionallypredictive-coded picture, is coded as an image to be inserted betweenthe I picture and the P picture after the I picture and the P pictureare processed in advance. In other words, the B picture utilizes thefollowing three kinds of pictures as a predicted image: 1) the I pictureor the P picture of an earlier time already decoded, 2) the I picture orthe P picture of a later time already decoded, and 3) an interpolatedimage made from 1) and 2).

[0020] Thus, video decode unit 6 cannot output an image signal until asequence header and an I picture is properly decoded. Moreover, in orderto adjust the output timing of audio decode unit 5 and video decode unit6 so as to ensure the synchronization between the image signal output toimage display unit 8 and the audio signal output to audio output unit 7,i.e. the AV synchronization, a certain amount of coded data must beaccumulated in audio decode unit 5 and video decode unit 6. As aconsequence, image display would also be delayed for the period duringwhich coded data required to ensure the AV synchronization isaccumulated. The delay of the image display upon power-on or uponchannel switching due to these factors may be expected to amount toabout two to three seconds.

[0021] On the other hand, as a user is selecting a channel, when aspecific channel that the user wishes to view cannot be found, the usertends to manipulate the channel selection by selecting the channelsinstantly and continuously in order to grasp in a short time thecontents of broadcast on the respective channels. Hereinafter, suchchannel selecting manipulation would also be referred to as a “channelsampling manipulation.”

[0022] It is likely that the “channel sampling manipulation” that theuser routinely performs with the analog television broadcast cannot beperformed smoothly with the digital television broadcast due to theinfluence of delay in the image display upon channel switching describedabove. Particularly, after the user inputs a channel switchinginstruction, a period created during which no image signal is output byimage display unit 8 is very likely to cause the user discomfort due tounnecessary anxiety and stress.

SUMMARY OF THE INVENTION

[0023] An object of the present invention is to provide a digitalbroadcast receiving apparatus that provides an appropriate image displayupon power-on or upon channel switching until the display of the normalreal time images corresponding to the selected channel becomes possibleso as to prevent causing discomfort to the user.

[0024] According to the present invention, a digital broadcast receivingapparatus for selectively receiving a desired channel based on a userinstruction from a plurality of channels included in airwaves includes afirst tuning unit for extracting from the airwaves first image codeddata that corresponds to the desired channel, a second tuning unit forsuccessively selecting one of the plurality of channels as a backgroundchannel and extracting from the airwaves second image coded data thatcorresponds to the background channel, a data storage unit for storingthe second image coded data that correspond to the respective ones ofthe plurality of channels, a control unit for determining whether it ispossible or impossible to generate an image signal based on the firstimage coded data, and a first image data decoding unit for decoding thesecond image coded data from the data storage unit to generate an imagesignal for image display when image display based on the first imagecoded data is impossible in accordance with the determination of thecontrol unit.

[0025] Preferably, the digital broadcast receiving apparatus furtherincludes a first data selecting unit for receiving the first image codeddata from the first tuning unit and the second image coded data from thedata storage unit corresponding to the desired channel and selectivelyoutputting one of the first image coded data and the second image codeddata according to the determination of the control unit. The first imagedata decoding unit decodes an output from the first data selecting unitto generate an image signal.

[0026] Preferably, the digital broadcast receiving apparatus furtherincludes a second image data decoding unit for decoding the second imagecoded data extracted by the second tuning unit, and an image data codingunit for recoding the second image coded data decoded by the secondimage data decoding unit. The data storage unit stores the second imagecoded data recoded by the image data coding unit, and the recoded secondimage coded data has a smaller amount of data than the second imagecoded data extracted by the second tuning unit.

[0027] Preferably, the digital broadcast receiving apparatus furtherincludes a data buffer unit for temporarily accumulating the imagesignal output from the first image data decoding unit, an image datacoding unit for recoding the image signal, a first data selecting unitfor selectively outputting the image signal output by the first imagedata decoding unit to one of the data buffer unit and the image datacoding unit according to the determination of the control unit, and asecond data selecting unit for receiving the first image coded data fromthe first tuning unit and the second image coded data from the datastorage unit corresponding to the desired channel, and the second imagecoded data from the second tuning unit corresponding to the backgroundchannel, and for outputting to the first image data decoding unit one ofthe first image coded data, the second image coded data from the datastorage unit, and the second image coded data from the second tuningunit according to the determination of the control unit. The datastorage unit stores the image signal recoded by the image data codingunit as the second image coded data, and the recoded second image codeddata has a smaller amount of data than the second image coded dataextracted by the second tuning unit.

[0028] According to the digital broadcast receiving apparatus of thepresent invention, immediately after channel switching and the like, theimage coded data corresponding to a video image of the past of thedesired channel stored within in advance as a background channel can beread so as to display the video image until the display of a real timevideo image corresponding to a desired channel becomes possible. As aresult, even when the user switches the channel selection successively,the video image display would not be interrupted so that the user wouldnot experience any discomfort.

[0029] Moreover, the contents of the image coded data stored inside inadvance for the respective channels are successively updated in aconstant cycle so that the user can grasp the contents of broadcast onthe respective channels in a short time by successive switching of thechannel selection.

[0030] In addition, the data storage unit stores as image coded datacorresponding to the background channel the image signal recoded to asmaller amount of data so that the data storage unit can be reduced insize.

[0031] According to another aspect of the present invention, a digitalbroadcast receiving apparatus for selectively receiving a desiredchannel based on a user instruction from a plurality of channelsincluded in airwaves includes a tuning unit for extracting from theairwaves first image coded data that corresponds to the desired channel,a data storage unit for storing second image coded data for displaying aprescribed picture, a control unit for determining whether it ispossible or impossible to generate an image signal based on the firstimage coded data, and an image data decoding unit for decoding thesecond image coded data from the data storage unit to generate an imagesignal for image display when the image display based on the first imagecoded data is impossible in accordance with the determination of thecontrol unit.

[0032] Preferably, the digital broadcast receiving apparatus furtherincludes a data selecting unit for receiving the first image coded datafrom the tuning unit and the second image coded data from the datastorage unit corresponding to the desired channel and selectivelyoutputting one of the first image coded data and the second image codeddata according to the determination of the control unit. The image datadecoding unit decodes an output from the data selecting unit to generatean image signal.

[0033] Moreover, according to the digital broadcast receiving apparatusof the present invention, the image coded data corresponding to aprescribed picture stored within in advance can be read so as to displaythe video image until the display of a real time video imagecorresponding to a desired channel becomes possible. As a result, evenwhen there is only one tuning unit that has a tuner function, the videoimage display would not be interrupted immediately after power-on orimmediately after channel switching, so that the user would notexperience any discomfort.

[0034] The foregoing and other objects, features, aspects and advantagesof the present invention will become more apparent from the followingdetailed description of the present invention when taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0035]FIG. 1 is a block diagram related to the description of a mainportion related to image signal processing of digital broadcastreceiving apparatus according to a first embodiment of the presentinvention.

[0036]FIG. 2 is a flow chart related to the description of a controloperation of a control unit 40 upon switching of channel selection by auser.

[0037]FIG. 3 is a timing chart related to the description of an exampleof an operation of digital broadcast receiving apparatus according tothe first embodiment.

[0038]FIG. 4 is a block diagram related to the description of a mainportion related to image signal processing of digital broadcastreceiving apparatus according to a second embodiment of the presentinvention.

[0039]FIG. 5 is a block diagram related to the description of a mainportion related to image signal processing of digital broadcastreceiving apparatus according to a modification of the second embodimentof the present invention.

[0040]FIG. 6 is a block diagram related to the description of a mainportion related to image signal processing of digital broadcastreceiving apparatus according to a third embodiment of the presentinvention.

[0041] FIGS. 7 to 10 are block diagrams related to the description of amain portion related to image signal processing of digital broadcastreceiving apparatus according to first to fourth modifications of thethird embodiment of the present invention.

[0042]FIG. 11 is a schematic block diagram representing an arrangementof a general digital television broadcast receiving system.

[0043]FIG. 12 is a schematic diagram related to the description of acomposition of image coded data according to MPEG2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0044] The embodiments of the present invention will be described indetail below with reference to the drawings.

[0045] First Embodiment

[0046] Referring to FIG. 1, a digital broadcast receiving apparatus 10according to the first embodiment of the present invention includes aninput terminal 11 a for receiving RF signals which are the airwavesreceived by an antenna 2, an input terminal 11 b for receiving usermanipulation such as power-on and channel selection, and an outputterminal 11 c for outputting to an image display unit 8 an image signalcorresponding to a desired channel selected by the user. The usermanipulation that is input to input terminal 11 b may be input from auser control unit integrally provided with digital broadcast receivingapparatus 10 by a panel or the like, or may be input using a remotecontrol from outside digital broadcast receiving apparatus 10 byinfrared rays or the like.

[0047] Digital broadcast receiving apparatus 10 further includes tuningunits 18 a and 18 b for extracting the image coded data corresponding toa prescribed channel from the RF signals. Tuning unit 18 a includes atuner 12 a for tuning according to a channel selecting signal CSL1, ademodulating unit 14 a for demodulating a signal selected by tuner 12 a,and a transport stream decoder (hereinafter, referred to as a TSdecoder) 16 a for converting a demodulated signal into TS data.

[0048] Similarly, tuning unit 18 b includes a tuner 12 b for performingtuning according to a channel selecting signal CSL2, a demodulating unit14 b for demodulating a signal selected by tuner 12 b, and a TS decoder16 b for converting a demodulated signal into TS data. Consequently, TSdecoders 16 a and 16 b extract a baseband signal corresponding to aselected channel.

[0049] Provision of two systems of tuning units 18 a and 18 b allows thereceiving operation to be performed for background reproduction as willbe described later, even while an image corresponding to the userdesired channel is being displayed on image display unit 8. Tuning unit18 a performs, according to channel selecting signal CSL1, the tuningcorresponding to the desired channel selected by the user. On the otherhand, tuning unit 18 b performs in the background, according to channelselecting signal CSL2, the tuning corresponding to channels that aresuccessively selected independently of the user desired channel.

[0050] In the arrangement of FIG. 1, of the TS data which are coded dataaccording to the MPEG2 standard output from TS decoders 16 a and 16 b,only the arrangement related to image coded data is illustrated. TSdecoder 16 a outputs image coded data VCDa corresponding to the desiredchannel, and TS decoder 16 b outputs image coded data VCDb received inthe background.

[0051] When performing the reproduction based on an image signalobtained by decoding image coded data VCDa from tuning unit 18 a, theuser desired channel can be extracted from the airwaves and a real timeimage can be displayed. Hereinbelow, the image display based on imagecoded data VCDa is also referred to as normal reproduction. On the otherhand, the image display based on image coded data VCDb from tuning unit18 b is also referred to as background reproduction.

[0052] When digital broadcast receiving apparatus 10 is to be providedwith a multi-channel display feature for providing multiple display of aplurality of channels on image display unit 8, a multiple systems oftuning units inevitably becomes necessary. Thus, in digital broadcastreceiving apparatus 10 having the multi-channel display feature, one ofa plurality of systems of tuning units arranged may be used for thebackground receiving operation when the multi-channel display feature isnot selected.

[0053] Digital broadcast receiving apparatus 10 further includes an MPEGvideo decode unit 20, a control unit 40 for controlling an imageprocessing operation in digital broadcast receiving apparatus 10, and aninterface unit 45 for transmitting to control unit 40 the usermanipulation input to input terminal 1 b.

[0054] Digital broadcast receiving apparatus 10 further includes amemory unit 30 for recording image coded data received in thebackground. Memory unit 30 has a plurality of memory regions MA1 to MAnrespectively corresponding to n channels (n is a natural number) thatare receivable. Memory unit 30 performs writing, storing, and reading ofdata in response to a memory control signal CMD which is generated bycontrol unit 40.

[0055] Digital broadcast receiving apparatus 10 further includes a dataselector 31 for selectively transmitting image coded data VCDb outputfrom TS decoder 16 b to one of memory regions MA1 to MAn, a dataselector 32 for outputting one of image coded data output respectivelyfrom memory regions MA1 to MAn, and a data selector 34. Data selector 34outputs to MPEG video decode unit 20 one of image coded data VCDa outputfrom TS decoder 16 a and image coded data VCDb output from data selector32.

[0056] MPEG video decode unit 20 includes a decode LSI for decodingimage coded data transmitted from data selector 34, a work memory usedas a buffer to store data temporarily, and so on, which are not shown.

[0057] Control unit 40 generates a channel selecting signal CSL1 basedon user channel selection, a channel selecting signal CSL2 periodicallyfor switching a background channel independent of the user channelselection, a reproduction data selecting signal SLV for selecting a dataoutput in data selector 34, and memory control signal CMD forcontrolling the operation of memory unit 30.

[0058] Channel selecting signal CSL1 is set corresponding to a desiredchannel selected by the user. Channel selecting signal CSL2 is set toallow periodical and successive selection of one of n channels that canbe received as a background channel independently of the user channelselection.

[0059] Data selector 31 transmits image coded data VCDb output fromtuning unit 18 b to a memory region corresponding to the backgroundchannel in memory unit 30 according to channel selecting signal CSL2.Control unit 40 instructs the data write to memory unit 30 at a timingthat coincides with the timing at which image coded data VCDb istransmitted from data selector 31.

[0060] In this manner, in memory unit 30, image coded data correspondingto the past pictures received in the background are stored as backgrounddata respectively corresponding to the n channels that are receivable.The background data corresponding to the respective channels areperiodically updated according to channel selecting signal CSL2.

[0061] As background data, image coded data of an I picture, forinstance, may be stored as static image data. In addition, the I pictureand a B picture and a P picture related to the I picture may be combinedand stored as motion image data of a very brief duration.

[0062] When the channel selection is switched through user manipulation,control unit 40 changes the setting of channel selecting signal CSL1. Inresponse to this change, tuning unit 18 a starts generating image codeddata VCDa corresponding to a newly selected channel Hereinafter, alsoreferred to as a post-switching channel). Before the normal reproductioncorresponding to the post-switching channel becomes possible, however, acertain time period is required until the generated image coded dataVCDa reaches a certain amount.

[0063] MPEG video decode unit 20 monitors the generation status of imagecoded data VCDa corresponding to the post-switching channel in TSdecoder 16 a, and generates a flag signal RDY indicating whether thenormal reproduction corresponding to the post-switching channel ispossible. Flag signal RDY is reset to the logic low or the L level inresponse to switching of the channel selection. Until image coded dataVCDa generated by TS decoder 16 a reaches a certain amount that allowsthe normal reproduction, flag signal RDY is maintained at the L level.

[0064] Control unit 40 instructs the execution of backgroundreproduction during the period in which flag signal RDY is at the Llevel (hereinafter, also referred to as a normal reproduction waitperiod).

[0065] Control unit 40 instructs memory unit 30 to perform reading ofbackground data stored in memory regions MA1 to MAn in response toswitching of the channel selection. Data selector 32 selects backgrounddata output from memory unit 30 according to channel selecting signalCSL1, and outputs to data selector 34 image coded data VCDb thatcorresponds to the post-switching channel.

[0066] Control unit 40 generates reproduction data selecting signal SLVin response to a signal level of flag signal RDY that indicates whethernormal reproduction is possible. In other words, during the normalreproduction wait period in which normal reproduction is not ready to beperformed, reproduction data selecting signal SLV instructs dataselector 34 to output image coded data VCDb to perform backgroundreproduction. Consequently, even when the image display by normalreproduction cannot be provided immediately after channel switching, thedisplay of a past image corresponding to the post-switching channel canbe provided so that discomfort can be removed for the user.

[0067] Since tuning by tuning unit 18 a and demodulation operation areperformed in parallel with the background reproduction, normalreproduction would become possible after at least a certain amount ofimage coded data VCDa corresponding to the post-switching channel havebeen generated. MPEG video decode unit 20 changes the signal level offlag signal RDY from the L level to the logic high or the H level whenthe normal reproduction becomes possible.

[0068] Accordingly, control unit 40 switches the signal level ofreproduction data selecting signal SLV. In response, data selector 34switches the image coded data to be transmitted to MPEG video decodeunit 20 from image coded data VCDb for background reproduction to imagecoded data VCDa for normal reproduction. Thereafter, the signal levelsof flag signal RDY and reproduction data selecting signal SLV aremaintained until a new channel switching manipulation is input. In thismanner, when data selector 34 is provided and the image coded data to besupplied to MPEG video decode unit 20 are switched, MPEG video decodeunit 20 can be shared by normal reproduction and backgroundreproduction.

[0069] Referring to FIG. 2, when user performs the manipulation toswitch the channel selection (step S100), control unit 40 updateschannel selecting signal CSL1 according to the user channel selection(step S110). Moreover, control unit 40 instructs MPEG video decode unit20 to reset (to the L level) flag signal RDY (step S120).

[0070] Control unit 40 monitors the signal level of flag signal RDY tocheck whether normal reproduction corresponding to the post-switchingchannel is possible (step S130). When normal reproduction is not readyto be performed, reproduction data selecting signal SLV is set to the Llevel, and image coded data VCDb which is the background data outputfrom data selector 32 is sent to MPEG video decode unit 20 (step S140).As a result, background reproduction is performed during the normalreproduction wait period. Step 140 is performed repeatedly until thenormal reproduction becomes possible.

[0071] When the normal reproduction is ready to be performed and thesignal level of flag signal RDY changes to the H level, control unit 40changes the signal level of reproduction data selecting signal SLV fromthe L level to the H level (step S15O). Accordingly, image coded dataVCDa from TS decoder 16 a is transmitted to MPEG video decode unit 20.Consequently, the normal reproduction corresponding to thepost-switching channel is performed (step S160).

[0072] Such operation of control unit 40 can be processed using softwarebased on a program recorded in a ROM (Read Only Memory) and the like,for instance. In addition, hardware corresponding to the flow chartshown in FIG. 2 may be provided.

[0073] Now, an example of an operation of digital broadcast receivingapparatus 10 will be described using FIG. 3.

[0074] Referring to FIG. 3, a channel ch1 is selected before time t0,and at time t0, the channel selection is switched from channel ch1 to achannel ch2. Moreover, it is assumed that, at time t1, the channelselection is switched from channel ch2 to a channel ch4, and at time t2,from channel ch4 to a channel 5.

[0075] Channel selecting signal CSL1 is set according to the userchannel selection. In other words, channel selecting signal CSLL selectschannels ch1, ch2, ch4, and ch5 before time t0, from time t0 to time t1,from time t1 to time t2, and after time t2, respectively.

[0076] Channel selecting signal CSL2 periodically switches the channelselection independently of the user channel selection. FIG. 2 shows thecase where the number of receivable channels is five, and five channelsch1 to ch5 are selected periodically by channel selecting signal CSL2.

[0077] Image coded data VCDb output from tuning unit 18 b according tochannel selecting signal CSL2 is stored in memory unit 30 as backgrounddata. The background data of the respective channels are updated in aconstant cycle. For instance, the background data corresponding tochannel ch2 is updated from CH2 a to CH2 b at time t2. In this manner,background data corresponding to the respective channels areperiodically and successively updated in memory regions MA1 to MAnwithin memory unit 30.

[0078] Although not shown, reproduction data selecting signal SLV isreset from the H level to the L level at time t0 when the channelswitching is performed. From time t0 to time t1 and from time t1 to timet2, new channel switching manipulation is executed before normalreproduction is made ready so that the signal level of reproduction dataselecting signal SLV is maintained at the L level.

[0079] Accordingly, prior to time t0, image display unit 8 displaysimages corresponding to CH1 which is the normal reproduction data ofchannel ch1. Then, from time t0 to time t1, an image based on backgrounddata CH2 a corresponding to channel ch2 is displayed on image displayunit 8. Similarly, from time t1 to time t2, an image based on backgrounddata CH4 a corresponding to channel ch4 is displayed on image displayunit 8.

[0080] After time t2, no new channel switching manipulation is input sothat, at a time t3 when normal reproduction becomes ready, the signallevel of reproduction data selecting signal SLV changes from the L levelto the H level corresponding to the change of flag signal RDY. Thus,from time t2 to time t3, image display unit 8 displays an image based onbackground data CH5 a of channel ch5, and after time t3, displays imagesbased on normal reproduction data CH5 corresponding to channel ch5.

[0081] In this manner, even when the user performs channel switchingwith short intervals, it becomes possible to display successive imagescorrespondingly. Particularly, the period from time t0 to time t3 inwhich the display based on background data is performed is a period inwhich the image display based on the received airwaves is impossible ina normal digital broadcast receiving apparatus so that, by successivelyproviding image display during this period, the discomfort caused to theuser can be eliminated. In addition, the background data is successivelyand periodically updated so that the content of the background data canbe approximated to the content of a picture according to normalreproduction. Consequently, the so-called channel sampling manipulationthat the user performs in order to grasp the contents of broadcast onthe respective channels in a short time can be dealt with.

[0082] In addition, while the selection of the background channels isperformed uniformly with all the receivable channels in the firstembodiment, it is also possible to specify the target of selection ofbackground channels to a part of all the receivable channels. In thiscase, for instance, part of the channels to be the target of selectionof background channels can be designated based on the selectionfrequency of the respective channels and the selecting patterns of theuser in the past.

[0083] Second Embodiment

[0084] Referring to FIG. 4, a digital broadcast receiving apparatus 50according to the second embodiment of the present invention differs fromdigital broadcast receiving apparatus 10 shown in FIG. 1 in that itfurther includes an MPEG video decode unit 21 and an MPEG video encodeunit 25 provided corresponding to background data.

[0085] MPEG video decode unit 21 first decodes image coded data VCDboutput by tuning unit 18 b in order to generate background data. MPEGvideo encode unit 25 recodes image coded data VCDb decoded by MPEG videodecode unit 21 and outputs image coded data VCDb′. Memory unit 30 storesthe recoded image coded data VCDb′ as the background data.

[0086] At this time, the recoding in MPEG video encode unit 25 isperformed such that the amount of image coded data VCDb′ after recodingis smaller than the amount of image coded data VCDb as output fromtuning unit 18 b. For instance, the resolution upon recoding may be setlower than the resolution corresponding to normal reproduction data soas to limit the capacity of the background data stored in memory unit30.

[0087] Consequently, the memory capacity of memory unit 30 can be mademore compact than in the case of digital broadcast receiving apparatus10 shown in FIG. 1. As a result, reduction in cost and in size of thedigital broadcast receiving apparatus can be achieved.

[0088] The arrangement in other portions of digital broadcast receivingapparatus 50 and the operations thereof are the same as those of digitalbroadcast receiving apparatus 10 shown in FIG. 1 so that the descriptionthereof will not be repeated.

[0089] Modification to Second Embodiment

[0090] Referring to FIG. 5, a digital broadcast receiving apparatus 51according to a modification of the second embodiment of the presentinvention differs from digital broadcast receiving apparatus 50 shown inFIG. 4 in that digital broadcast receiving apparatus 51 is not providedwith MPEG video decode unit 21 and that digital broadcast receivingapparatus 51 further includes a data selector 36 and a data buffer 22 assubsequent stages to MPEG video decode unit 20.

[0091] The arrangement in other portions of digital broadcast receivingapparatus 51 and the operations thereof are the same as those of digitalbroadcast receiving apparatus 50 shown in FIG. 4 so that the descriptionthereof will not be repeated.

[0092] In digital broadcast receiving apparatus 51, the process ofdecoding the image coded data corresponding to background data asdescribed with FIG. 4 is performed using MPEG video decode unit 20.

[0093] Thus, in addition to image coded data VCDa from tuning unit 18 aand image coded data VCDb corresponding to the background data from dataselector 32, the recoded image coded data VCDb′ from tuning unit 18 b isalso input to data selector 34.

[0094] Data selector 34 outputs one of image coded data VCDa, VCDb, andVCDb′ to MPEG video decode unit 20 according to a reproduction dataselecting signal SLV′.

[0095] By successively decoding image coded data from data selector 34,MPEG video decode unit 20 performs the decoding processing of data fornormal reproduction and data for background reproduction to be displayedon image display unit 8 along with the decoding processing for limitingthe amount of the background data to be stored in memory unit 30.

[0096] Thus, according to a reproduction data selecting signal SLV″,when MPEG video decode unit 20 decodes image coded data VCDa for normalreproduction and image coded data VCDb′ for background reproduction tobe displayed on image display unit 8, data selector 36 outputs thedecoded image signal to data buffer 22. On the other hand, when MPEGvideo decode unit 20 decodes image coded data VCDb for generatingbackground data to be stored in memory unit 30, data selector 36 outputsthe decoded image signal to MPEG video encode unit 25.

[0097] As in the case shown in FIG. 4, MPEG video encode unit 25performs recoding such that the amount of data is reduced from imagecoded data VCDb prior to decoding. As a result, like the case shown inFIG. 4, the memory capacity of memory unit 30 can be made small.

[0098] Thus, when the throughput of MPEG video decode unit 20 issufficiently high, an arrangement may be adopted which allows temporarystorage of the image signal to be sent to image display unit 8 in databuffer 22 so that the capacity of memory unit 30 can be made smallerwithout additionally providing an MPEG video decode unit.

[0099] Third Embodiment

[0100] The first and second embodiments describe the arrangements inwhich the reproduction of background data of the respective channelsthat are periodically updated is performed when normal reproduction isimpossible. In other words, the digital broadcast receiving apparatusesaccording to the first and second embodiments inevitably require aplurality of tuner systems (tuning units). The third embodimentdescribes an arrangement that allows picture display during the normalreproduction wait period in relation to the case where a single tunersystem (tuning unit) is provided.

[0101] Referring to FIG. 6, a digital broadcast receiving apparatus 60according to the third embodiment of the present invention includes aninput terminal 11 a for receiving RF signals which are the airwavesreceived by an antenna 2, an input terminal 11 b for receiving usermanipulation, an output terminal 11 c for outputting to an image displayunit 8 an image signal corresponding to a desired channel selected bythe user, a tuning unit 18 a for performing normal reproduction, a dataselector 34, and an MPEG video decode unit 20. Tuning unit 18 a includesa demodulating unit 14 a and a TS decoder 16 a.

[0102] Digital broadcast receiving apparatus 60 further includes acontrol unit 40, an interface unit 45 for transmitting to control unit40 the user manipulation input to input terminal 11 b, and a memory unit30. A channel selecting signal CSL1 is set according to a desiredchannel selected by the user.

[0103] During the normal reproduction wait period, digital broadcastreceiving apparatus 60 outputs an image signal for displaying aprescribed static image or motion image on image display unit 8. Theprescribed picture displayed during the normal reproduction wait periodwill hereinafter also be referred to as a reception wait picture. Memoryunit 30 stores image coded data for the reception wait picture storedbefore shipment.

[0104] When power-on or a channel switching instruction via interfaceunit 45 is detected, control unit 40 instructs memory unit 30 to outputimage coded data VCDb for the reception wait picture as well as switchesto the data output path that is different from the data output path usedfor normal reproduction in data selector 34 until a flag signal RDY fromMPEG video decode unit 20 is set to the signal level indicating thatnormal reproduction has become possible. Accordingly, data selector 34outputs image coded data VCDb from memory unit 30 to MPEG video decodeunit 20.

[0105] Thereafter, when the normal reproduction by MPEG video decodeunit 20 becomes possible, control unit 40 switches data output selectionof data selector 34 in response to the change of flag signal RDY andsends image coded data VCDa from TS decoder 16 a to MPEG video decodeunit 20.

[0106] With such an arrangement, it becomes possible to display areception wait picture so as not to cause interruption in the imagedisplay even during the period in which normal reproduction isimpossible upon power-on, immediately after channel switching, and soon. As a result, the discomfort caused to the user can be alleviatedduring the normal reproduction wait period.

[0107] First Modification to Third Embodiment

[0108] Referring to FIG. 7, a digital broadcast receiving apparatus 61according to the first modification of the third embodiment of thepresent invention differs from digital broadcast receiving apparatus 60shown in FIG. 6 in that digital broadcast receiving apparatus 61 furtherincludes a timing unit 47. Timing unit 47 has the function of measuringat least one of the date and the time. Moreover, a memory unit 30 storesa plurality of image coded data respectively corresponding to aplurality of reception wait pictures.

[0109] A control unit 40 selects one of the plurality of image codeddata stored in memory unit 30 according to the time of day, the day ofweek, and the season based on the current time or date measured bytiming unit 47. In response to a memory control signal CMD and a pictureselecting signal DSL, memory unit 30 outputs to a data selector 34 imagecoded data VCDb for displaying the reception wait picture selected bycontrol unit 40.

[0110] With such an arrangement, it becomes possible to switch thedisplay of the reception wait picture automatically according to thecurrent date or time in digital broadcast receiving apparatus 61 so asto enhance its entertainment quality.

[0111] Second Modification to Third Embodiment

[0112] Referring to FIG. 8, a digital broadcast receiving apparatus 62according to the second modification of the third embodiment of thepresent invention differs from digital broadcast receiving apparatus 60shown in FIG. 6 in that digital broadcast receiving apparatus 62 furtherincludes data selectors 31 and 32 corresponding to a memory unit 30.

[0113] Digital broadcast receiving apparatus 62 stores in memory unit 30text information that a broadcast station had transmitted using databroadcast and the like and outputs the image signal to be displayed onimage display unit 8 as a reception wait picture during the normalreproduction wait period.

[0114] Thus, memory unit 30 includes memory regions MA1 to MAncorresponding to the respective channels. A TS decoder 16 a separatescoded data corresponding to the text information from image coded dataand the like and outputs the separated coded data to a data selector 31.Data selector 31 operates in response to a channel selecting signalCSL1, and stores the coded data from a tuning unit 18 b into a memoryregion corresponding to the received channel.

[0115] During the normal reproduction wait period upon power-on or uponchannel switching, the coded data corresponding to the channel currentlyselected by the user is sent from memory unit 30 to a data selector 34via a data selector 32 that operates according to channel selectingsignal CSL1. Thus, it becomes possible to display a reception waitpicture according to information received from text data broadcast andthe like.

[0116] Third Modification to Third Embodiment

[0117] Referring to FIG. 9, a digital broadcast receiving apparatus 63according to the third modification of the third embodiment of thepresent invention differs from digital broadcast receiving apparatus 60shown in FIG. 6 in that digital broadcast receiving apparatus 63 furtherincludes an MPEG video encode unit 25. MPEG video encode unit 25 codesan image signal output by an MPEG video decode unit 20 in response to acontrol signal CP generated by a control unit 40. Image coded data VCDcfrom MPEG video decode unit 20 is transmitted to a memory unit 30.Memory unit 30 stores image coded data VCDc as data for a reproductionwait picture.

[0118] Control signal CP is generated in response to a user instructioninput to an input terminal 11 b. Thus, it becomes possible for the userto capture any given static image or moving image from the display imagebeing broadcast and to adopt it as the reproduction wait picture.Moreover, memory unit 30 can be made more compact by lowering theresolution in the coding by MPEG video encode unit 25 from theresolution of the normal reproduction.

[0119] Fourth Modification to Third Embodiment

[0120] Referring to FIG. 10, a digital broadcast receiving apparatus 64according to the fourth modification of the third embodiment of thepresent invention differs from digital broadcast receiving apparatus 60shown in FIG. 6 in that a receiving condition signal JST from a tuner 12a is input to control unit 40. Tuner 12 a activates receiving conditionsignal JST when the input of the RF signals that are the airwavesreceived by an antenna 2 is interrupted, for instance, at a terminationof broadcast or when the video signal is interrupted.

[0121] In addition to the normal reproduction wait period, at the timewhen receiving condition signal JST is activated, control unit 40 readsimage coded data for displaying a reception wait picture to memory unit30 in order to display the wait picture. Further, control unit 40switches the setting of reproduction data selecting signal SLV such thatthe image coded data read from memory unit 30 is output by data selector34.

[0122] Consequently, in addition to the normal reproduction wait periodcorresponding to the power-on or the channel switching, even at thetermination of the broadcast or when input of the video signal isinterrupted, it becomes possible automatically to invoke and display areproduction wait picture on an image display unit.

[0123] Moreover, digital broadcast receiving apparatus 64 shown in FIG.10, in addition to an arrangement of digital broadcast receivingapparatus 60 according to the third embodiment, displays a receptionwait picture according to the receiving condition of the RF signals in atuner. A similar arrangement, however, can be applied to digitalbroadcast receiving apparatus 10 according to the first embodiment, todigital broadcast receiving apparatuses 50 and 51 according to thesecond embodiment and its modification, respectively, and to digitalbroadcast receiving apparatuses 61, 62, and 63 according to the first tothird modifications of the third embodiment, respectively.

[0124] Furthermore, the embodiments of the present invention has beendescribed with regard to an arrangement for receiving digital broadcastusing coded data according to the MPEG2 standard, the present inventionis similarly applicable to reception of digital broadcast according toother coding standard such as the MPEG1 standard, the MPEG4 standard,and a motion JPEG (Joint Photographic Experts Group) standard.

[0125] Although the present invention has been described and illustratedin detail, it is clearly understood that the same is by way ofillustration and example only and is not to be taken by way oflimitation, the spirit and scope of the present invention being limitedonly by the terms of the appended claims.

What is claimed is:
 1. A digital broadcast receiving apparatus forselectively receiving a desired channel based on a user instruction froma plurality of channels included in airwaves, comprising: a first tuningunit for extracting from said airwaves first image coded data thatcorresponds to said desired channel; a second tuning unit forsuccessively selecting one of said plurality of channels as a backgroundchannel and extracting from said airwaves second image coded data thatcorresponds to said background channel; a data storage unit for storingsaid second image coded data that correspond to the respective ones ofsaid plurality of channels; a control unit for determining whether it ispossible or impossible to generate an image signal based on said firstimage coded data; and a first image data decoding unit for decoding saidsecond image coded data from said data storage unit to generate an imagesignal for image display when said image display based on said firstimage coded data is impossible in accordance with the determination ofsaid control unit.
 2. The digital broadcast receiving apparatusaccording to claim 1, further comprising: a first data selecting unitfor receiving said first image coded data from said first tuning unitand said second image coded data from said data storage unitcorresponding to said desired channel and selectively outputting one ofsaid first image coded data and said second image coded data accordingto the determination of said control unit, wherein said first image datadecoding unit decodes an output from said first data selecting unit togenerate an image signal.
 3. The digital broadcast receiving apparatusaccording to claim 1, wherein said control unit determines whether it ispossible or impossible to generate an image signal based on an amount ofsaid first image coded data extracted by said first tuning unit.
 4. Thedigital broadcast receiving apparatus according to claim 3, wherein whenswitching of said desired channel by a user is detected, said controlunit sets an output from said first data selecting unit to said secondimage coded data until generation of said image signal based on saidfirst image coded data in said first image data decoding unit becomespossible, and from a time when the generation of said image signalbecomes possible, switches the output from said first data selectingunit, from said first image coded data to said second image coded data.5. The digital broadcast receiving apparatus according to claim 1,further comprising: a second image data decoding unit for decoding saidsecond image coded data extracted by said second tuning unit; and animage data coding unit for recoding said second image coded data decodedby said second image data decoding unit, wherein said data storage unitstores said second image coded data recoded by said image data codingunit, and the recoded second image coded data has a smaller amount ofdata than said second image coded data extracted by said second tuningunit.
 6. The digital broadcast receiving apparatus according to claim 5,wherein said image data coding unit executes said recoding based on asecond resolution that is lower than a first resolution that correspondsto said first image coded data.
 7. The digital broadcast receivingapparatus according to claim 3, further comprising: a data buffer unitfor temporarily accumulating said image signal output from said firstimage data decoding unit; an image data coding unit for recoding saidimage signal; a first data selecting unit for selectively outputtingsaid image signal output by said first image data decoding unit to oneof said data buffer unit and said image data coding unit according tothe determination of said control unit; and a second data selecting unitfor receiving said first image coded data from said first tuning unitand said second image coded data from said data storage unitcorresponding to said desired channel, and said second image coded datafrom said second tuning unit corresponding to said background channel,and for outputting to said first image data decoding unit one of saidfirst image coded data, said second image coded data from said datastorage unit, and said second image coded data from said second tuningunit according to the determination of said control unit, wherein saiddata storage unit stores said image signal recoded by said image datacoding unit as said second image coded data, and said recoded secondimage coded data has a smaller amount of data than said second imagecoded data extracted by said second tuning unit.
 8. The digitalbroadcast receiving apparatus according to claim 7, wherein said imagedata coding unit executes said recoding based on a second resolutionthat is lower than a first resolution that corresponds to said firstimage coded data.
 9. The digital broadcast receiving apparatus accordingto claim 1, wherein said control unit successively updates selection ofsaid background channel in a constant cycle.
 10. A digital broadcastreceiving apparatus for selectively receiving a desired channel based ona user instruction from a plurality of channels included in airwaves,comprising: a tuning unit for extracting from said airwaves first imagecoded data that corresponds to said desired channel; a data storage unitfor storing second image coded data for displaying a prescribed picture;a control unit for determining whether it is possible or impossible togenerate an image signal based on said first image coded data; and animage data decoding unit for decoding said second image coded data fromsaid data storage unit to generate an image signal for image displaywhen said image display based on said first image coded data isimpossible in accordance with the determination of said control unit.11. The digital broadcast receiving apparatus according to claim 10,further comprising: a data selecting unit for receiving said first imagecoded data from said tuning unit and said second image coded data fromsaid data storage unit corresponding to said desired channel andselectively outputting one of said first image coded data and saidsecond image coded data according to the determination of said controlunit, wherein said image data decoding unit decodes an output from saiddata selecting unit to generate an image signal.
 12. The digitalbroadcast receiving apparatus according to claim 11, wherein saidcontrol unit instructs to switch the output from said data selectingunit from said first image coded data to said second image coded dataaccording to receiving condition of said airwaves in said tuning unit.13. The digital broadcast receiving apparatus according to claim 10,wherein said data storage unit stores said second image coded databefore shipment of said digital broadcast receiving apparatus.
 14. Thedigital broadcast receiving apparatus according to claim 10, furthercomprising: a timing unit for detecting at least one of current date andcurrent time, wherein said data storage unit stores a plurality of saidsecond image coded data, and said control unit selectively outputs oneof said plurality of said second image coded data according to saiddetection by said timing unit.
 15. The digital broadcast receivingapparatus according to claim 10, wherein said data storage unit stores aplurality of said second image coded data respectively corresponding tosaid plurality of channels and outputs one of said plurality of saidsecond image coded data that corresponds to said desired channel. 16.The digital broadcast receiving apparatus according to claim 15, whereinsaid plurality of said second image coded data include text informationthat is multiplexed with image information and transmitted in saidairwaves.
 17. The digital broadcast receiving apparatus according toclaim 10, further comprising: an image data coding unit for recodingsaid image signal corresponding to a picture selected by a user, whereinsaid data storage unit stores the image signal recoded by said imagedata coding unit as said second image coded data.